The primary purpose of this study is to conclusively determine whether a causal relationship exists between the presence of dental amalgam restorations and elevated blood and mouth air mercury levels. This will be done by comparing the baseline levels in these media before and after the removal of existing amalgam restorations. Confounding factors such as exogenous exposure to mercury as well as ethanol an tobacco use will be accounted for using questionnaires. Approximately six weekly blood and mouth air determinations will be required to obtain a reliable measure of their preremoval levels. A statistical regime will be used in which the post removal data will be compared after each weekly sampling. Using this approach it is anticipated that definable changes will be evident before the maximum sampling duration has expired, i.e. three half times for whole body elemental mercury clearance (24 weeks). The results of this work are important to both the dental profession and the general public because of the ubiquitous use of dental amalgam as a restorative material. Data exists which indicates that dental amalgam restorations may be health hazards. If this is so then the magnitude of the problem may be large. Conversely, the benefit to the general public of the application of dental amalgam in terms of dental health must be considered. It is therefore imperative that the existence of a causal relationship between dental amalgams and the body burden of mercury be based on irrefutable evidence. The secondary purpose is to determine whether microstructural and compositional characteristics of amalgam specimens removed from participants in this study are related to their mercury volatilization. This will be done by measuring their phase distribution and composition with an ARL microprobe and their mercury volatilization with a spectrophotometer. These results will be compared for statistical correlation. The aim of this part of the proposed work is to improve dental amalgam with regard to its mercury emission rates.